Preparation of dialkyl-ansa-metallocenes

ABSTRACT

In a process for the racemoselective preparation of silicon-bridged dialkyl-ansa-metallocenes of the formula (I) comprises reaching a ligand starting compound of the formula (II) with a transition metal dialkyl compound of the formula (III) M 1 X x R 1   2 *D y  (III), where M 1  is an element of group 4, 5 or 6 of the periodic Table of the Elements, R 1  are identical C 1 -C 20 -alkyl or C 7 -C 40 -arylalkyl radicals, X are identical or different halogens, R 2  are identical or different C 1 -C 40  radicals, R 3  are identical or different C 1 -C 40  radicals, T is a divalent C 1 -C 40  group which together with the cyclopentadienyl ring forms a further saturated or unsaturated ring system which has a ring size of from 5 to 12 atoms, where T may contain the heteroatoms Si, Ge, N, P, O or S in the ring system fused onto the cyclopentadienyl ring, M 2  is Li, Na, K, MgCl, MgBr, MgI, Mg or Ca, D is an uncharged Lewis base ligand, x is equal to the oxidation number of M 1  minus 2, y is from 0 to 2 and p is 1 in the case of doubly positively charged metal ions or 2 in the case of singly positively charged metal ions or metal ion fragments.  
                 
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The present invention relates to a process for the racemoselectivepreparation of silicon-bridged dialkyl-ansa-metallocenes of the formula(I) and also to the use of a transition metal dialkyl compound of theformula (III) for the racemoselective preparation of these metallocenes.

The preparation of isotactic polypropylene (i-PP) is generally carriedout using ansa-metallocenes in their racemic form. Metallocenes whichhave been found to give particularly good performance and are thereforeindustrially relevant are substituted silicon-bridgedansa-bisindenylzirconocene dichlorides as described in EP-B 0 485 821,EP-A 0 549 900 or EP-A 0 576 970.

The catalyst system used for the polymerization of olefins usuallycomprises at least one metallocene and at least one cocatalyst, forexample a methylaluminoxane or a borate salt. When using a borate salt,for example [Ph₃C]⁺[B(C₆F₅)₄]⁻ or [HN(n-Bu)₃]⁺[B(C₆F₅)₄]⁻, ascocatalyst, the metallocenes are preferably used asdialkyl-metallocenes. The dialkyl-metallocenes have two alkyl radicalsbound to the transition metal.

Processes for synthesizing dialkyl-metallocenes are known. In U.S. Pat.No. 5,936,108, metallocene dichlorides such as zirconocene dichloridesare reacted with lithium alkyl compounds such as methyllithium, with thechloride ligands on the transition metal being replaced by alkylradicals. In EP-A 0 682 036, monomethyl- and dimethyl-metallocenes aresynthesized by reaction of the corresponding metallocene dichlorideswith trimethylaluminum in the presence of potassium fluoride.

In both processes, the previously synthesized metallocene dichloride isused as starting compound, so that the synthesis of racemicdimethyl-metallocenes requires the corresponding racemic metallocenedichlorides as starting compounds. However, the synthesis of thecorresponding ansa-metallocene dichlorides usually gives them as arac/meso mixture, so that the meso compound has to be separated off.

Journal of Organometallic Chemistry 535 (1997) 29-32 describes a processfor the synthesis of variously bridged dimethyl-bisindenylzircoceneswhich bear hydrogen in each of the 2 positions of the two indenylradicals. In this process, the doubly deprotonated bridged bisindenylligand is reacted with dimethylzirconium dichloride, which has to behandled at below −40° C. In the case of the synthesis ofdimethylsilylbisindenyldimethylzirconium, which bears hydrogen atoms inthe 2 positions on the two indenyl radicals, a meso-enriched productmixture was obtained, so that the meso product, which is here the mainproduct, would have to be separated off to obtain the rac isomer.

For the abovementioned reasons, the known methods of preparing racemicsilicon-bridged dialkyl-ansa-metallocenes leave something to be desiredin respect of economics and ability to be readily implemented inindustry.

It is an object of the present invention to find a process for preparingpredominantly racemic silicon-bridged dialkyl-ansa-metallocenes whichoffers advantages both from an economic point of view and also in termsof ability to be implemented in industrial production.

We have found that this object is achieved by a process for theracemoselective preparation of silicon-bridged dialkyl-ansa-metallocenesof the formula (I)

which comprises reacting a ligand starting compound of the formula (II)

with a transition metal dialkyl compound of the formula (111)M¹X_(x)R¹ ₂*D_(y)  (III),

-   -   where    -   M¹ is an element of group 4, 5 or 6 of the Periodic Table of the        Elements,    -   R¹ are identical C₁-C₂₀-alkyl or C₇-C₄₀-arylalkyl radicals,    -   X are identical or different halogens,    -   R² are identical or different C₁-C₄₀ radicals,    -   R³ are identical or different C₁-C₄₀ radicals,    -   T is a divalent C₁-C₄₀ group which together with the        cyclopentadienyl ring forms a further saturated or unsaturated        ring system which has a ring size of from 5 to 12 atoms, where T        may contain the heteroatoms Si, Ge, N. P, O or S in the ring        system fused onto the cyclopentadienyl ring,    -   M² is Li, Na, K, MgCl, MgBr, MgI, Mg or Ca,    -   D is an uncharged Lewis base ligand,    -   x is equal to the oxidation number of M¹ minus 2,    -   y is from 0 to 2 and    -   p is 1 in the case of doubly positively charged metal ions or 2        in the case of singly positively charged metal ions or metal ion        fragments.

Furthermore, the use of the transition metal dialkyl compound of theformula (III) for the racemoselective preparation of silicon-bridgeddialkyl-ansa-metallocenes of the formula (I) has been found.

M¹ is an element of group 3, 4, 5 or 6 of the Periodic Table of theElements or of the lanthanides, for example titanium, zirconium,hafnium, vanadium, niobium, tantalum, chromium, molybdenum or tungsten,preferably titanium, zirconium or hafnium, particularly preferablyzirconium or hafnium and very particularly preferably zirconium.

The radicals R¹ are identical and are each C₁-C₂₀-alkyl, preferablyC₁-C₅-alkyl, or C₇-C₄₀-arylalkyl, preferably C₇-C₁₅-arylalkyl, where thearyl part contains from 6 to 10, preferably 6, carbon atoms and thealkyl part preferably contains 1 carbon atom and the aryl part may besubstituted by further C₁-C₄-alkyl radicals. The radicals R¹ areparticularly preferably methyl or benzyl, in particular methyl.

The radicals X are identical or different, preferably identical, and areeach halogen, for example fluorine, chlorine, bromine or iodine,preferably chlorine.

The radicals R² are identical or different and are each a C₁-C₄₀ radicalwhich is preferably bound via a carbon atom to the cyclopentadienylligand and may be branched in the a position or unbranched. R² ispreferably a linear or branched C₁-C₂₀-alkyl radical, preferably aC₁-C₅-alkyl radical, particularly preferably a C₁-C₄-alkyl radical, oran arylalkyl radical having from 1 to 10, preferably from 1 to 4, carbonatoms in the alkyl part and from 6 to 22, preferably from 6 to 10,carbon atoms in the aryl part. Examples of very particularly preferredradicals R² are methyl, ethyl, n-propyl, isopropyl, n-butyl, i-butyl,n-pentyl, n-hexyl, benzyl and 2-phenylethyl.

Unless restricted further, alkyl is a linear, branched or cyclic radicalsuch as methyl, ethyl, n-propyl, isopropyl, n-butyl, i-butyl, s-butyl,t-butyl, n-pentyl, cyclopentyl, n-hexyl, cyclohexyl, n-heptyl orn-octyl.

The radicals R³ are identical or different and are each a C₁-C₄₀radical, for example a C₁-C₂₀-alkyl radical, preferably a C₁-C₄-alkylradical, a C₂-C₂₀-alkenyl radical, preferably a C₂-C₄-alkenyl radical, aC₆-C₂₂-aryl radical, preferably a C₆-C₁₀-aryl radical, an alkylaryl orarylalkyl radical having from 1 to 10, preferably from 1 to 4, carbonatoms in the alkyl part and from 6 to 22, preferably from 6 to 10,carbon atoms in the aryl part, where the radicals may also behalogenated. Examples of particularly preferred radicals R³ areC₁-C₄-alkyl, in particular methyl or ethyl, and phenyl.

T is a divalent C₁-C₄₀ group which together with the cyclopentadienylring forms a further saturated or unsaturated ring system which has aring size of from 5 to 12, preferably from 5 to 7, particularlypreferably 5 or 6, atoms, where T may contain the heteroatoms Si, Ge, N,P, O or S, preferably N or S, in the ring system fused onto thecyclopentadienyl ring.

M² is preferably Li, MgCl, MgBr or Mg, in particular Li.

The uncharged Lewis base ligand D can, for example, be a linear, cyclicor branched oxygen-, sulfur-, nitrogen- or phosphorus-containing,preferably oxygen-containing, hydrocarbon. Preference is given to ethersand polyethers such as diethyl ether, dibutyl ether, tert-butyl methylether, anisole, triglyme, tetrahydrofuran and dioxane. Particularpreference is given to 1,2-dimethoxyethane and tetrahydrofuran.

Particular preference is given to a process for the racemoselectivepreparation of silicon-bridged dialkyl-ansa-metallocenes of the formula(I),

in which

-   -   T is a 1,3-butadiene-1,4-diyl group Which may be unsubstituted        or be substituted by from 1 to 4 radicals R⁴, where the two        1,3-butadiene-1,4-diyl groups may be different,    -   R⁴ are identical or different C₁-C₂₀ radicals,    -   M¹ is titanium, zirconium or hafnium,    -   R¹ are identical C₁-C₅-alkyl or C₇-C₂₀-arylalkyl radicals,    -   X is halogen and    -   R², R³, M², D, p, x and y are as defined above.

Preference is given to M¹ being zirconium and R¹ being methyl.

The 1,3-butadiene-1,4-diyl groups T are identical or different,preferably identical.

The radicals R⁴ on the substituted 1,3-butadiene-1,4-diyl groups T areidentical or different, in particular identical, and are each a C₁-C₂₀radical such as a C₁-C₄-alkyl radical or a substituted or unsubstitutedC₆-C₄₀-aryl radical. The radicals R⁴ are particularly preferablysubstituted or unsubstituted C₆-C₄₀-aryl radicals having from 1 to 10,preferably from 1 to 4, carbon atoms in the alkyl part and from 6 to 22,preferably from 6 to 10, carbon atoms in the aryl part, where theradicals may also be halogenated. Examples of preferred radicals R⁴ arephenyl, 2-tolyl, 3-tolyl, 4-tolyl, 2,3-dimethylphenyl,2,4-dimethylphenyl, 2,5-dimethylphenyl, 2,6-dimethylphenyl,3,4-dimethylphenyl, 3,5-dimethylphenyl, 3,5-di(tert-butyl)phenyl,2,4,6-trimethylphenyl, 2,3,4-trimethylphenyl, 1-naphthyl, 2-naphthyl,phenanthrenyl, p-isopropylphenyl, p-tert-butylphenyl, p-s-butylphenyl,p-cyclohexylphenyl and p-trimethylsilylphenyl.

The number of radicals R⁴ on the substituted 1,3-butadiene-1,4-diylgroups T is preferably 1 or 2, in particular 1.

The 1,3-butadiene-1,4-diyl group T together with the cyclopentadienylradical forms an indenyl system which is, in particular, substituted inthe 2,4 positions, 2,4,5 positions, 2,4,6 positions or 2,4,7 positions,where two substituents on the six-membered ring of the indenyl systemmay together be part of a further ring system, for example a further1,3-butadiene-1,4-diyl group. The indenyl systems are very particularlypreferably substituted in the 2,4 positions.

The substitution pattern indicated in the example of the process of thepresent invention is most preferred.

In the process of the present invention, the salt-like ligand startingcompounds of the formula (II) are prepared either in isolated form insitu immediately before the reaction with the transition metal dialkylcompound of the formula (III).

To synthesize the salt-like ligand starting compounds of the formula(II), the corresponding uncharged silicon-bridged biscyclopentadienylcompound is doubly deprotonated by means of a strong base. Strong baseswhich can be used are, for example, organolithium or organomagnesiumcompounds such as methyllithium, n-butyllithium, sec-butyllithium,n-butyl-n-octylmagnesium or dibutylmagnesium.

The uncharged silicon-bridged biscyclopentadienyl compound to bedeprotonated can once again be used in isolated form or withoutisolation directly from the bridging reaction of two cyclopentadienylanions with an appropriate silicon reagent, for example adiorganodichlorosilane such as dimethyldichlorosilane. A furtherpossible way of preparing the uncharged silicon-bridgedbiscyclopentadienyl compounds is a stepwise route. In this case, forexample, a cyclopentadienyl anion is reacted with an appropriate siliconreagent, for example a diorganodichlorosilane such asdimethyldichlorosilane, to form amonochloromonocyclopentadienyldiorganosilane compound and the chlorinein this is subsequently replaced by a further cyclopentadienyl group,which may be different from the first, to obtain the desired unchargedsilicon-bridged biscyclopentadienyl compound.

The synthesis of the cyclopentadienyl anions can in principle be carriedout under the same conditions as the deprotonation of the unchargedsilicon-bridged biscyclopentadienyl compound.

The double deprotonation of the uncharged silicon-bridgedbiscyclopentadienyl compound to form the ligand starting compound of theformula (II) is usually carried out in the temperature range from −78°C. to 110° C., preferably from 0° C. to 80° C. and particularlypreferably from 20° C. to 60° C. Suitable inert solvents in which thedeprotonation of the cyclopentadienyl derivatives by means of strongbases can be carried out are aliphatic or aromatic hydrocarbons such asbenzene, toluene, xylene, mesitylene, ethylbenzene, cumene, decalin,tetralin, pentane, hexane, cyclohexane or heptane or ethers such asdiethyl ether, di-n-butyl ether, tert-butyl methyl ether (MTBE),tetrahydrofuran (THF), 1,2-dimethoxyethane (DME), anisole, triglyme ordioxane and also any mixtures of these materials. Preference is given tosolvents or solvent mixtures in which the subsequent process of thepresent invention for preparing the metallocene complexes of the formula(I) can likewise be carried out.

In an embodiment of the process of the present invention, the transitionmetal dialkyl compound of the formula (III) is produced at above −30°C., in particular above 0° C., by combining a compound M¹X_(x+2) withfrom 2 to 2.5 equivalents of a compound R¹M³ in the presence of a ligandcompound D, whereM³ is Li⁺, Na⁺, K⁺, MgCl⁺, MgBr⁺, MgI⁺, ½[Mg⁺⁺] or ½[Zn⁺⁺], andthe other variables are as defined above.

In another embodiment of the process of the present invention, theligand starting compound of the formula (II) is combined with thetransition metal dialkyl compound of the formula (III) at above −30° C.,preferably above 0° C.

After the reaction components have been combined, the reaction mixtureis preferably maintained at from 30° C. to 150° C., in particular from50° C. to 80° C.; for a period of at least 10 minutes, preferably from 1to 8 hours.

In a further embodiment of the process of the present invention, thereaction is carried out in an organic solvent or solvent mixture whichcomprises at least 10% by volume, preferably at least 50% by volume,particularly preferably at least 80% by volume, very particularlypreferably at least 90% by volume, of an ether, in particular a cyclicether. An example of a very useful ether is tetrahydrofuran. Furtherinert solvents which may be present in the reaction solution are theabovementioned aliphatic or aromatic hydrocarbons or ethers in which thedeprotonation of the ligand can be carried out.

In the process of the present invention, it is possible for not only thedesired rac compounds of the formula (I) but also the corresponding mesocompounds to be formed. In those cases in which the two cyclopentadienylradicals on the silicon bridge are not identical, the compound does notexist in a meso form having C_(s) symmetry or rac form having C₂symmetry, but instead there are only diastereomeric compounds having C₁symmetry. In cases in which the two cyclopentadienyl radicals areidentical but the two radicals R³ on the silicon bridge are notidentical, the compound exists as a racemic diastereomer having C₁symmetry and two different meso diastereomers having C_(s) symmetry.When used as catalyst components in the polymerization of propylene,these different diastereomeric metallocene compounds which differ fromone another in the three-dimensional arrangement of the varioussubstituents behave, solely on the basis of the three-dimensionalarrangement of the two cyclopentadienyl ligands relative to one another,like the C₂-symmetric rac isomers (isotactic polypropylene) or like theC_(s)-symmetric meso isomer (atactic polypropylene) and can thus each bedesignated as a pseudo-rac form or a pseudo-meso form.

In the following, rac and pseudo-rac form and meso and pseudo-meso formwill be differentiated only as rac form and meso form.

In a further embodiment of the process of the present invention, theracemoselectivity (proportion of rac−proportion of meso)/(proportion ofrac+proportion of meso) is greater than zero, preferably greater than0.5.

The invention further provides for the use of the transition metaldialkyl compound of the formula (III) for the racemoselectivepreparation of silicon-bridged dialkyl-ansa-metallocenes of the formula(I) as described above.

Illustrative but nonlimiting examples of metallocenes of the formula (I)are:

-   dimethylsilanediylbis(2-methyl-4-phenylindenyl)dimethylzirconium,-   dimethylsilanediylbis(2-methyl-4,5-benzoindenyl)dimethylzirconium,-   dimethylsilanediylbis(2-methyl-4-(4′-tert-butylphenyl)indenyl)dimethylzirconium,-   dimethylsilanediylbis(2-ethyl-4-(4′-tert-butylphenyl)indenyl)dimethylzirconium,-   dimethylsilanediylbis(2-n-propyl-4-(4′-tert-butylphenyl)indenyl)dimethylzirconium,-   dimethylsilanediyl(2-methyl-4-(4′-tert-butylphenyl) indenyl)    (2-isopropyl-4-(4′-tert-butylphenyl)indenyl)dimethylzirconium,-   dimethylsilanediyl(2-ethyl-4-(4′-tert-butylphenyl)indenyl)(2-isopropyl-4-(4′-tert-butylphenyl)indenyl)dimethylzirconium,-   dimethylsilanediyl(2-methyl-4-phenylindenyl)(2-isopropyl-4-(4′-tert-butylphenyl)indenyl)dimethylzirconium,-   dimethylsilanediyl(2-isopropyl-4-(4′-tert-butylphenyl)-1-indenyl)(2,7-dimethyl-4-(4′-tert-butylphenyl)indenyl)dimethylzirconium,-   dimethylsilanediyl(2-isopropyl-4-(4′-tert-butylphenyl)-1-indenyl)(2-ethyl-7-methyl-4-(4′-tert-butylphenyl)indenyl)dimethylzirconium.

The salts of the formula M²X or M²X₂, for example lithium chloride ormagnesium chloride, which are obtained as coproduct in the process ofthe present invention for preparing racemic silicon-bridgeddialkyl-ansa-metallocenes of the formula (I) can be separated off fromthe metallocene by known methods. For example, a salt such as lithiumchloride can be precipitated by means of a suitable solvent in which themetallocene, however, is soluble, so that the solid lithium chloride isseparated off from the dissolved metallocene by means of a filtrationstep. The metallocene can also be separated off from the salt byextraction with a suitable solvent of this type. Any such filtrationsteps can also be carried out using filter aids such as kieselguhr. Forexample, organic solvents, in particular organic aprotic, oxygen-freesolvents such as toluene, ethylbenzene, xylenes or methylene chloride,can be used for such a filtration or extraction step. If necessary, thesolvent components in which the salt is at least partly soluble areremoved to a substantial extent before the salt is separated off asdescribed above. For example, lithium chloride is appreciably soluble intetrahydrofuran.

The racemic silicon-bridged dialkyl-ansa-metallocenes of the formula (I)prepared by the process of the present invention are used as catalystconstituents together with suitable cocatalysts and, if appropriate,suitable support materials in the catalyst systems for thehomopolymerization or copolymerization of α-olefins.

EXAMPLES

General

All experiments using organometallic compounds were carried out in bakedglass vessels and under a protective argon atmosphere.

1 Synthesis of Me₂Si(2-Me-4-PhInd)₂ZrMe₂

1a Synthesis of Dimethylzirconium Dichloride (1)

356 ml of THF were placed in a reaction vessel at 0° C. and 4.97 g ofzirconium tetrachloride (21.3 mmol) were added. At 0°, 47 ml of 1Mmethyllithium solution in cumene/THF (47 mmol=2.2 eq) were addeddropwise over a period of 8 minutes. The yellow solution wassubsequently stirred for another 30 minutes at 0° C.

1b Synthesis of Me₂Si(2-Me-4-PhInd)₂ZrMe₂ (2)

10 g of dimethylbis(2-methyl-4-phenyl-1-indenyl)silane (21.3 mmol) weredissolved in 236 ml of THF, cooled to 0° C. and 18.8 ml of butyllithiumsolution (2.5 molar in toluene, corresponding to 47 mmol=2.2 eq) wereadded dropwise over a period of 4 minutes. The cold bath was removed andthe reaction mixture was stirred for another 25 minutes (T=15° C.). Thereddish brown reaction mixture was added at 0° C. to the solution ofdimethylzirconium dichloride prepared in Experiment 1a over a period of15 minutes and the resulting mixture was subsequently heated to 65° C.

After 4.5 hours at 65° C., about 90% of the solvent (596 ml) weredistilled from the brown suspension. The proton NMR of a sample of thecrude product indicated a rac/meso ratio of 3:1. 375 ml of toluene weresubsequently added to the crude product suspension and the suspensionwas stirred at 60° C. for 30 minutes, filtered through a G3 protectivegas frit and the residue was washed once with 50 ml of warm toluene (60°C.).

The filtrate was evaporated to about Y % of its volume (125 ml) and thesolid formed was filtered off via a G3 protective gas frit. Theyellowish green residue was washed twice with 3 ml of toluene and driedin an oil pump vacuum.

Yield: 3.86 g of (2) as a yellow solid; pure rac isomer according toproton NMR (corresponds to 31% of the theoretical yield)

1. A process for the racemoselective preparation of silicon-bridgeddialkyl-ansa-metallocenes of the formula (I)

which comprises reacting a ligand starting compound of the formula (II)

with a transition metal dialkyl compound of the formula (III)M¹X_(x)R¹ ₂*D_(y)  (III), where M¹ is an element of group 4, 5 or 6 ofthe Periodic Table of the Elements; R¹ are identical C₁-C₂₀-alkyl orC₇-C₄₀-arylalkyl radicals; X are identical or different halogens; R² areidentical or different C₁-C₄₀ radicals; R³ are identical or differentC₁-C₄₀ radicals; T is a divalent C₁-C₄₀ group which together with thecyclopentadienyl ring forms a further saturated or unsaturated ringsystem which has a ring size of from 5 to 12 atoms, where T may containthe heteroatoms Si, Ge, N, P, O or S in the ring system fused onto thecyclopentadienyl ring; M² is Li, Na, K, MgCl, MgBr, MgI, Mg or Ca; D isan uncharged Lewis base ligand; x is equal to the oxidation number of M¹minus 2; y is from 0 to 2; and p is 1 in the case of doubly positivelycharged metal ions or 2 in the case of singly positively charged metalions or metal ion fragments.
 2. Ah process as claimed in claim 1,wherein T is a 1,3-butadiene-1,4-diyl group which may be unsubstitutedor be substituted by from 1 to 4 radicals R⁴, where the two1,3-butadiene-1,4-diyl groups may be different; R⁴ are identical ordifferent C₁-C₂₀ radicals; M¹ is titanium, zirconium or hafnium; R¹ areidentical C₁-C₅-alkyl or C₇-C₂₀-arylalkyl radicals; and X is halogen. 3.The process as claimed in claim 1, wherein the transition metal dialkylcompound of the formula (III) is produced at above −30° C. by combininga compound M¹X_(x+2) with from 2 to 2.5 equivalents of a compound R¹M³in the presence of a ligand compound D, where M³ is Li⁺, Na⁺, K⁺, MgCl⁺,MgBr⁺, MgI⁺, ½[Mg⁺⁺] or ½[Zn⁺⁺].
 4. The process as claimed in claim 1,wherein the ligand starting compound of the formula (II) is combinedwith the transition metal dialkyl compound of the formula (III) at above−30° C.
 5. The process as claimed in claim 4, wherein a reaction mixtureis maintained at from 30° C. to 150° C. for a period of at least 10minutes after the reaction components have been combined.
 6. The processas claimed in claim 1, wherein the reaction is carried out in an organicsolvent or solvent mixture which comprises at least 10% by volume of anether.
 7. The process as claimed in claim 1, wherein aracemoselectivity=(proportion of rac−proportion of meso)/(proportion ofrac+proportion of meso) is greater than zero.
 8. A process comprisingutilizing a transition metal dialkyl compound of the formula (III):M¹X_(x)R¹ ₂*D_(y)  (III) for the racemoselective preparation ofsilicon-bridged dialkyl-ansa-metallocenes of the formula (1):

wherein M¹ is an element of group 4, 5 or 6 of the Periodic Table of theElements; R¹ are identical C₁-C₂₀-alkyl or C₇-C₄₀-arylalkyl radicals; Xare identical or different halogens; R² are identical or differentC₁-C₄₀ radicals; R³ are identical or different C₁-C₄₀ radicals; D is anuncharged Lewis base ligand; y is from 0 to 2; T is a divalent C₁-C₄₀group which together with the cyclopentadienyl ring forms a furthersaturated or unsaturated ring system which has a ring size of from 5 to12 atoms, where T may contain the heteroatoms Si, Ge, N, P, O or S inthe ring system fused onto the cyclopentadienyl ring; and x is equal tothe oxidation number of M¹ minus
 2. 9. The process as claimed in claim2, wherein the transition metal dialkyl compound of the formula (III) isproduced at above −30° C. by combining a compound M¹X_(x+2) with from 2to 2.5 equivalents of a compound R¹M³ in the presence of a ligandcompound D, whereM³ is Li⁺, Na⁺, K⁺, MgCl⁺, MgBr⁺, MgI⁺, ½[Mg⁺⁺] or ½[Zn⁺⁺].
 10. Theprocess as claimed in claim 2, wherein the ligand starting compound ofthe formula (II) is combined with the transition metal dialkyl compoundof the formula (III) at above −30° C.
 11. The process as claimed inclaim 10, wherein a reaction mixture is maintained at from 30° C. to150° C. for a period of at least 10 minutes after the reactioncomponents have been combined.